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Yes, parts joined before Cortec has cured will be adhered from Cortec, and therefore difficult to separate if you ever need to take them apart. The biggest advantage I found with Cortec was that it is water soluble, doesn't have nasty fumes, and is easy to apply with a cheap foam brush.
I started off using Cortec but have switched over to spray primer (Akzo-Nobel). I have been very pleased with the decision. I think the protection is much better. I think Cortec is good, but primer (at least Akzo) is better.
Success of priming is surface preparation for 95 %, more than the kind of primer itself. I use a good deagreser, cleaning with aluprep solution and finaly rince with water. I use the expoxy Dupond formula primer with success since 15 years. The main purpose of the primer is not stick pieces together, if pieces have to move, they will crack the paint, stick together or not. The primer paint add no resistance at all to the structure, and they are not part of calculation resistance in the factor load calculated by CH or any other ingeneer. Alu is no wood or fabric.
CH640 from plan 0059
the priming issue is periodically brought up and everyone has their own ideas. I shot a video of my thoughts way back in 2017, I just reviewed it and my thoughts are exactly the same. If you are interested here is the link https://youtu.be/DZjz8_7gPYY . Dan.
I liked the convenience of Cortec. Had a quart can from Zenith which is way more than enough to prime all mating surfaces, so that meant no trips to the store to buy rattle cans of primer, no masking-off to prevent overspray, and no clogged nozzles! I also liked that Cortec was non-toxic and you can dilute it with water. Caleb, the engineer that used to be at Zenith, told me to just dilute a small amount with water to a consistency that would spread a thin film when applied. I used disposable foam brushes for convenience. I would put a dollop in a small plastic lab specimen container like that used for urine samples at the doctor's office, dilute it and apply it, and then cap the container and any remainder was good for use next time - no waste!
Cortec, if not allowed to dry, will glue mating surfaces together, but as previously mentioned, it's there as a primer and not a structural glue. Caleb told me it was perfectly OK to rivet surfaces together if the Cortec wasn't dry, but don't do it on anything that you are temporarily fastening with clecos and then plan to disassemble again - you'll deform thin aluminum pieces before the dried Cortec releases. As long as you apply a thin film (which is all that is necessary), properly diluted Cortec will dry fairly quickly.
My firewall is now complete and I'd like to paint it a light color. Should have had it primed before completion but now what do I do.
1. I understand the firewall is not aluminum but some other metal for fire protection - anyone know what it is?
2. Now that it is complete it would be very difficult to clean all the parts and get into all the small areas, etc.
I believe the Zenith-supplied firewalls are galvanized steel. Stainless is also used for firewalls. I've seen comments that paint won't adhere well to galvanized metal. I've also seen comments that it's generally not a good idea to paint or powder coat the firewall - you're just adding another potentially flammable material that even if it doesn't burn, will char and create smoke in the event of an engine fire. Personally, I just left mine bare and 9 years later, it looks fine - no corrosion.
The firewall in my 601XL kit is galvanized steel. My plan is to leave it plain unpainted galvanized both to keep weight down (every little bit of primer and paint adds weight and it does add up in the course of a build) and because, as John pointed out, you don't want a combustilbe or fume generating surface on your firewall.
My 1948 Stinson 108-3 left the factory almost 73 years ago with a bare galvanized steel firewall and it still looks fine to this day.
John and Bob
I'm a beginner as this is my first build so I defer to your judgement. I have a fellow coming over tomorrow to provide comments on painting the cockpit - the firewall will remain unpainted.
Appreciate the advice.